North Korea must have expected this, having been similarly rebuked twice for missile and nuclear launches in 2006.

Yet Pyongyang professed high dudgeon at what was in truth mild UN Security Council remonstrance: just a statement, not a full resolution.

On this flimsy pretext, in a fine show of pique it repudiated the six-party talks and said it would resume its nuclear programme.

Monday's nuclear test showed this to be no idle threat. But why? Why now? What is really going on?

Less well known is that four separate high-level US delegations - nominally private but including Stephen Bosworth, now the Obama administration's point man on North Korea - visited Pyongyang earlier this year.

All got a frosty reception. Their hosts professed no interest in full relations with the US, long regarded as the ultimate prize sought by Kim Jong-il.

So how does this latest North Korean jigsaw - with too few and misshapen pieces, as always - fit together?

Stringing along

There are two broad possibilities and variants within either of those.

What message is Kim Jong-il trying to send, and to whom? Getting Obama's attention is one widely-touted suggestion. Yet on closer inspection this hardly adds up.

Barking louder than ever may be their way of scaring us off while they effect a delicate transition

Everyone knew, because he told us, that Barack Obama was ready to engage with America's foes. He means it, and he is doing it. With Cuba and others, change is already under way.

So surely this is the US President Kim Jong-il has been waiting for? True, Obama is busy with the Middle East and the financial crisis. But his door, and mind, are open.

It did not need a bomb or rocket to blast a way in and get a hearing in Washington. To the contrary, these were bound to backfire.

There have to be more Security Council resolutions and maybe sanctions, however ineffectual, when a rogue state makes a mockery of international law.

Kim Jong-il is no fool. So we must conclude, definitively now, that he has no intention of emulating Libya's Colonel Gaddafi and ever giving up his weapons of mass destruction.

The six long years of the six-party talks were just stringing us along. Without nuclear weapons, North Korea would be just another miserable tyranny. With them, it commands attention - if not respect.

Or maybe Kim Jong-il would have made peace, but hardliners used his illness last year to seize the helm and batten down the hatches.

Yet abandoning diplomacy altogether is hardly a serious long-term option, for a failed state reliant on Chinese aid to feed its hungry people.

Making peace would bring financial rewards to the impoverished state

Provoking Beijing is a risky game. A patient patron hitherto, China may finally snap and pull the plug on so tiresome a client - as Moscow did in 1991, devastating the North's economy.

Is the new turn merely tactical? If so, it is a dire miscalculation. Mr Kim's old game of militant mendicancy - doing bad things, to be paid to stop - will no longer wash. Everyone is fed up.

More exactly, the Dear Leader could have cleaned up if (and only if) he stuck with the six-party talks.

Peace and real disarmament would bring North Korea huge financial rewards: $10bn (£6.3bn) for full relations with Japan, and surely much more from a relieved Seoul.

One faint hope is that they may not really mean all this. That brings us to the second broad hypothesis.

Succession plan?

Rather than being any kind of odd signal to the wider world, North Korea's new militancy might be primarily driven by internal events, largely invisible to outside eyes.

Perverse as it sounds, barking louder than ever may be their way of scaring us off while they effect a delicate transition.

This could be a smokescreen behind which, not before time, one of Kim's mysterious and untried sons is being wheeled into place as his eventual successor.

If so, we may get more sense out of Pyongyang once such internal ructions settle down. But to speculate thus may be clutching at straws.

The view that North Korea is a rational actor - if only we are patient and avoid upsetting them - looks, let's face it, increasingly threadbare.

My fear is that defining itself against the world is hardwired into North Korea's outlook.

For over a decade, Bill Clinton, former South Korean President Kim Dae-jung, China, Russia and others strove to lead this most stubborn and suspicious of mules to water. But none could make it drink, beyond a few sips.

A toe in the water is as far as Kim Jong-il will ever go, on economic reform and peace alike. When it comes to the crunch, he refuses the fence.

At the risk of flogging equine metaphors to death, some blame the likes of George W Bush - before his U-turn to engagement - for frightening the horses with "axis of evil" rhetoric, so reinforcing Pyongyang's paranoia.

But ultimately, the choice and fault is Kim's. China and Vietnam show there is another way - the only way. North Korea is on a road to nowhere.

Aidan Foster-Carter is honorary senior research fellow in sociology and modern Korea at Leeds University

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